JP2000033131A - Manufacture of hollow golf ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method for a hollow golf ball whose hollow part is a complete sphere and excellent in durability. SOLUTION: This golf ball is composed of a hollow core 5 consisting of a hollow center 2 having a hollow part 1 and a middle layer 3 formed in one or more layers if necessary and a cover formed on the hollow core 5. In this case, a process for producing the hollow center 2 contains a process for forming the hollow center 2 where an adhering nonvulcanized rubber composition is arranged between the joining faces of two vulcanized cup-shaped hemispherical bodies to mutually stick them and the above nonvulcanized rubber composition is vulcanized in a metal mold, and the above composition is characterized by requiring the time of 5-20 minutes until a torque measured with a curastometer becomes as much as 90% of the maximum torque under a condition that the form of a test piece is 43 mm in diameter and 3 mm in thickness and a measuring temperature is the same as a vulcanizing temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow golf ball and a method of manufacturing the same, and more particularly, to a method of manufacturing a hollow golf ball having a true hollow hollow portion and excellent durability.

[0002]

2. Description of the Related Art In the prior art, there are mainly two types of golf balls. One is a solid golf ball such as a solid two-piece ball or a three-piece ball, and the other is a thread-wound golf ball. Solid golf balls are more durable than thread-wound golf balls, have a larger ball launch angle, and have a smaller backspin, so they have a longer flight distance and are more excellent in flight performance, especially for amateur golfers. Used by golfers. Therefore, the development of golf balls has been shifted from thread wound golf balls to solid golf balls in terms of increasing their flight distance. On the other hand, solid golf balls have a hard feeling when hit,
Lack of feeling when hit. However, recently, there is a solid golf ball that emphasizes the feeling at the time of hitting, but since the ball must be softened because the feeling at the time of hitting is emphasized, the resilience characteristics decrease and the flight performance decreases. There was a problem that it would.

Therefore, in a solid golf ball,
As a method of further increasing the flight distance, a method has been proposed in which the center portion is made hollow to increase the moment of inertia, thereby reducing the initial spin and decreasing the spin decay during flight (Japanese Utility Model Laid-Open No. 3-63354). ). As a method for producing such a golf ball, a rubber bowl-shaped hemisphere is produced by press molding or injection molding using a core mold,
A method of vulcanizing and bonding individual bowl-shaped hemispheres in a mold is conceivable (Japanese Patent Laid-Open No. 9-308709), but the hollow portion is deformed due to the thermal expansion of the rubber during post-vulcanization, resulting in a true spherical shape. Instead, the thickness of the core varies. Also, in the case of a hollow core made by bonding the hollowed-out hemisphere after vulcanization with an adhesive or the like, the impact at the time of hitting with a golf club is very large, and it is broken at the bonding surface and the durability is low. There is a problem that the temperature is extremely reduced.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the conventional hollow golf ball, and provides a method of manufacturing a hollow golf ball having a true spherical hollow portion and excellent durability. The purpose is to provide.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have arranged an unvulcanized rubber composition between the joining surfaces of two vulcanized bowl-shaped hemispheres. And bonding, and vulcanizing in a mold to form a hollow center, the method for producing a hollow golf ball, the unvulcanized rubber composition, using a curastometer, the sample shape is diameter The torque measured under the condition of 43 mm x 3 mm thickness and the measurement temperature is the same as the above vulcanization temperature is the maximum torque
By defining a time t ₉₀ until 90% within a specific range, the hollow portion is kept to a sphere, and found that the hollow golf ball having excellent durability can be obtained, thereby completing the present invention Reached.

That is, the present invention provides a hollow core (5) comprising a hollow center (2) having a hollow portion (1) and, if necessary, one or more intermediate core layers (3) formed on the hollow center. ), A method of manufacturing a hollow golf ball comprising a cover (4) formed on the hollow core, wherein the step of producing the hollow center comprises: (a) a step of preparing a rubber composition for the hollow center; A) forming a vulcanized bowl-shaped hemisphere using the rubber composition for a hollow center; and (c) disposing an unvulcanized rubber composition between the joining surfaces of the two bowl-shaped hemispheres. And vulcanizing the unvulcanized rubber composition in a mold to form a hollow center. The unvulcanized rubber composition is a circular sample having a diameter of 43 mm and a thickness of 3 mm. And the torque when measured at the same temperature as the vulcanization temperature in step (c) using a curast meter Of large torque 90
%. The method for producing a hollow golf ball, characterized in that the time (t ₉₀ ) until the percentage reaches 5% is 5 to 20 minutes.

The structure of the golf ball of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of one embodiment of the hollow golf ball of the present invention. As shown in FIG. 1, the golf ball of the present invention comprises a hollow center (2) having a hollow portion (1) and, if necessary, one or more intermediate core layers (3) formed on the hollow center. It comprises a hollow core (5) and a cover (4) formed on the hollow core.

Next, a method for manufacturing a hollow golf ball of the present invention will be described with reference to the drawings. FIG. 2 is a schematic sectional view of one embodiment of a mold used for manufacturing the hollow center (2) of the hollow golf ball of the present invention. As shown in FIG. 2, a rubber composition for a hollow center is inserted into a hemispherical mold (11) for forming a bowl-shaped hemisphere and a core (12) for a hollow portion, and is heated and pressed. A vulcanized bowl-shaped hemisphere (13) is produced. The heating press conditions for the bowl-shaped hemisphere are 140-180 ° C., preferably 150-180 ° C.
170170 ° C. for 10-60 minutes, preferably 15-20 minutes. If the vulcanization temperature is lower than 140 ° C., the vulcanization time becomes longer and the productivity is reduced, and if it is higher than 180 ° C., the rubber is liable to deteriorate.

The rubber composition used for the hollow center (2) contains a base rubber, a co-crosslinking agent, a cross-linking agent, a filler and the like. As the base rubber, a natural rubber, a synthetic rubber, or a mixture thereof, which has been conventionally used for a solid golf ball, is used. Examples of the synthetic rubber include polybutadiene rubber, polyisoprene rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPD).
M). Especially cis-1,4-structure at least 40%
The so-called high cis polybutadiene rubber having at least 80% is preferred. The base rubber comprises at least 70%, preferably 90%, of the rubber composition for high resilience.

Examples of the co-crosslinking agent include metal salts of unsaturated carboxylic acids, especially zinc and magnesium salts of α, β-unsaturated carboxylic acids having 3 to 8 carbon atoms such as acrylic acid or methacrylic acid. Valent or divalent metal salts,
In order to provide high resilience, zinc acrylate is used in the present invention. The amount is 15 to 5 parts per 100 parts by weight of the base rubber.
0 parts by weight, preferably 25 to 35 parts by weight are preferred. If it is more than 50 parts by weight, it will be too hard, and the feel when hitting will be poor. If it is less than 15 parts by weight, rebound will be poor and the flight distance will be reduced.

As a crosslinking agent, an organic peroxide such as dicumyl peroxide, 1,1-bis (t-butylperoxy)-
3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di
(t-butylperoxy) hexane, di-t-butyl peroxide, and the like, with dicumyl peroxide being preferred. The amount is 0.1 to 3 parts by weight, preferably 0.5 to 2.0 parts by weight, based on 100 parts by weight of the base rubber. If the amount is less than 0.1 part by weight, it becomes too soft, the rebound is deteriorated, and the flight distance is reduced. If it exceeds 3 parts by weight, it will be too hard, and the feel when hitting will be poor.

The filler may be any one as long as it is usually compounded in the core of a golf ball. For example, an inorganic salt (specifically,
Zinc oxide, barium sulfate, calcium carbonate), high specific gravity metal powder (for example, tungsten powder, molybdenum powder, etc.) and mixtures thereof. Since the weight of the hollow core used in the present invention tends to be less than that of a normal solid core, it is preferable to use a mixture of an inorganic salt and a high specific gravity metal powder.

The hollow center of the golf ball of the present invention further comprises an organic sulfur compound, an antioxidant or a peptizer,
In addition, components that can be generally used for manufacturing a core of a solid golf ball may be appropriately compounded. The antioxidant is 0.2
~ 0.5 parts by weight is preferred.

An unvulcanized rubber composition for bonding is arranged and bonded between the joining surfaces of the two bowl-shaped hemispheres manufactured as described above, and a hollow center forming hemisphere as shown in FIG. The unvulcanized rubber composition is vulcanized in a mold composed of two molds (21) to form a hollow center (2). The hollow center forming hemispherical mold (21) may be the same as or different from the above-described bowl-shaped hemispherical forming hemispherical mold (11). If different, use a hemispherical mold for hollow center molding (2
When the inner diameter of the cavity of 1) is larger, a gap is generated between the bowl-shaped hemisphere and the mold, the temperature transmission is reduced, and the vulcanization of the unvulcanized rubber composition for bonding becomes insufficient. Insufficient pressure on the unvulcanized rubber composition tends to cause poor adhesion. Also, if the cavity inner diameter of the hollow center forming hemispherical mold (21) is smaller, when the bonded bowl-shaped hemisphere thermally expands, the whole is subjected to pressure and the hollow portion is deformed. Therefore, the difference between the inner diameter of the hollow center forming hemispherical mold (21) and the inner diameter of the bowl-shaped hemispherical forming hemispherical mold (11) is -0.02.
0.00.02 mm, preferably −0.01 to 0.01 mm. Further, it is optimal that both molds have the same cavity inner diameter.

[0015] The vulcanized bowl-shaped hemisphere is thermally expanded due to the vulcanization temperature. Thereafter, an unvulcanized rubber composition for bonding is disposed between the joining surfaces of the two bowl-shaped hemispheres. When they are bonded together, they are cooled and shrunk, so that when they are inserted into the hollow center vulcanizing mold, there is a considerable gap between them. If vulcanization starts in such a state, since the hollow center does not completely contact the cavity of the mold, pressure is not applied to the entire hollow center, and a sufficient adhesive effect between the bowl-shaped hemispheres cannot be obtained. In addition, the durability of the hollow center is significantly reduced. Therefore, the vulcanization of the unvulcanized rubber composition for bonding starts after the hollow center thermally expands and completely contacts the cavity of the mold, so that a sufficient bonding effect is obtained.
It is necessary to delay the vulcanization time of the unvulcanized rubber composition.

For the above-mentioned reason, the unvulcanized rubber composition for bonding used in the present invention has a time t until the torque measured by using a curast meter becomes 90% of the maximum torque.
It is necessary to have _{90 to} 20 minutes, preferably 10 to 15 minutes. If t ₉₀ is shorter than 5 minutes, would be to proceed vulcanization of the unvulcanized rubber composition before the hollow center is expanded enough heat, the adhesive effect is insufficient, if longer than 20 minutes, pressure It is necessary to set the sulfurizing time longer, and the productivity decreases. Specific measuring method of determining the t _90, using a curastometer (Co. Orientec made of JSR Curastometer III D type), vulcanization temperature in step (c), i.e. vulcanization mold of Vibration given to the sample under the conditions that the set temperature is the measurement temperature of the above curast meter, sample shape diameter 43 mm x thickness 3 mm (circular sample), amplitude angle ± 1 degree, cycle 100 cpm (100 reciprocations per minute) Stress in response to
That is, the change with time of the torque is measured. FIG. 4 is a graph showing the change over time in torque from the unvulcanized state of the measured sample to complete vulcanization, and shows that as the torque increases, vulcanization progresses and the material becomes harder. Vulcanization torque with the inter gradually increases, appears maximum value T _max of the torque at the time t ₁₀₀ to vulcanization completed. The time until the torque of the sample reaches 90% of this maximum torque T _max (T _max × 0.9) and t _90.

The vulcanization time of the bowl-shaped hemispherical unvulcanized rubber composition for adhesion, when set to a time exceeding the t _90, the vulcanization of the unvulcanized rubber composition is complete, a bowl-shaped hemispherical The bonding of the body is also completed. The difference between the cure time and t ₉₀ is preferably at least 2 minutes, more preferably set to at least 4 minutes. Further, only between difference between too long unnecessarily vulcanizing the t ₉₀ is long, the difference between the cure time and t ₉₀ is preferably not more than 15 minutes, more preferably equal to or less than 10 minutes . Vulcanization conditions are:
The vulcanization temperature is 150-180 ° C, preferably 150-170 ° C,
The vulcanization time is between 10 and 30 minutes, preferably between 15 and 25 minutes.
If the vulcanization temperature is lower than 150 ° C., the vulcanization time becomes longer and the productivity decreases, and if it is higher than 180 ° C., the physical properties of the vulcanized rubber deteriorate. If the vulcanization time is shorter than 10 minutes, usable formulations are limited, leading to an increase in cost. If the vulcanization time is longer than 30 minutes, the productivity is reduced.

Further, in order to improve the above-mentioned bonding effect,
An unvulcanized rubber composition for bonding is arranged and bonded between the joining surfaces of the two bowl-shaped hemispheres, and the unvulcanized rubber composition is not vulcanized in a hollow center vulcanizing mold. Temperature, 100-130
C., preferably at 110-120 ° C. for 2 minutes or more, preferably 3 min.
After heating for 5 minutes to thermally expand, the unvulcanized rubber composition may be vulcanized under the above vulcanization conditions to form the hollow center (2).

The rubber composition used for bonding the bowl-shaped hemisphere is basically made of the same compounding material as the rubber composition for the hollow center. However, when the compounding amount of the organic peroxide increases, the vulcanization rate increases, and a sufficient adhesive effect cannot be obtained as described above. For the purpose of adjusting the vulcanization time of the unvulcanized rubber composition so as to be delayed, a phenolic antioxidant or an organic sulfur compound may be added. Examples of such antioxidants include, but are not limited to, Nocrack NS5 and Nocrack NS6 manufactured by Ouchi Shinko Chemical Co., Ltd. Examples of the organic sulfur compound include, but are not limited to, Ouchi Shinko Chemical Co., Ltd.
Manufactured by Barnock R and the like. A preferred composition of the rubber composition used for bonding the bowl-shaped hemisphere is a base rubber.
15 to 50 parts by weight of co-crosslinking agent and 0.1 of crosslinking agent for 100 parts by weight
5.0 parts by weight, filler 3-50 parts by weight and antioxidant 0.1
To 5.0 parts by weight.

The unvulcanized rubber composition for bonding a bowl-shaped hemisphere used in the present invention is preferably used in the form of a sheet or a solution of an organic solvent in view of the durability of the hollow center obtained. From the point of view, it is preferable to use in a solution state. The thickness of the unvulcanized rubber composition is 0.01 to 1.
0 mm, preferably 0.1 to 0.5 mm. If the thickness is less than 0.01 mm, the adhesive strength decreases. If the thickness is more than 1.0 mm, the polymer flows into the hollow portion during heating under pressure, the moment of inertia decreases, and the initial spin rate increases. In this case, the thickness of the unvulcanized rubber composition refers to the thickness of the sheet before pressing and heating in the case of a sheet, and refers to the thickness after application in the case of a solution.

The bowl-shaped hemisphere is not necessarily required to have a shape obtained by dividing the hollow center into two equal parts. Any kind may be used, and only one kind of bowl-shaped hemisphere prepared and stored for manufacturing the hollow center may be used, which is excellent in productivity. Thus, the bowl-shaped hemisphere is preferably formed into a shape obtained by dividing the hollow center into two equal parts.

The hollow core (5) may be constituted only by the hollow center (2), but one or more intermediate core layers (3) may be arranged on the hollow center. When the intermediate core layer (3) is used, a rubber composition similar to that used for the hollow center described above can be used for the intermediate core layer. By disposing the intermediate core layer (3), it is also possible to use different rubber compositions on the inside and outside of the hollow core, and various adjustments to improve the shot feeling and resilience of the obtained golf ball Becomes possible. In addition, since the expansion amount during vulcanization increases as the thickness of the rubber composition of the hollow center increases,
Compared to the case where the hollow core is formed only with the hollow center,
The thickness of the hollow center can be reduced. Therefore, in the manufacturing method of the hollow golf ball of the present invention, the unvulcanized rubber composition for bonding is arranged and bonded between the bonding surfaces of the vulcanized bowl-shaped hemispheres, and the uncured rubber composition is placed in a mold. In the step of vulcanizing the vulcanized rubber composition, there is also an effect that deformation of the hollow center and the hollow portion due to expansion of the rubber composition can be further prevented. Conversely, when the hollow core is composed of only the hollow center, the number of manufacturing steps is small and the productivity is excellent.

The diameter of the hollow part (1) is not particularly limited, but is 8 to 20 mm, preferably 10 to 15 mm.
When the diameter of the hollow portion is larger than 20 mm, the resulting golf ball is excessively deformed at the time of hitting, so that the energy loss is increased and the resilience is likely to be reduced. Further, it is necessary to use a large amount of filler for adjusting the specific gravity in the core rubber layer, and the resilience is reduced. When the diameter of the hollow portion is smaller than 8 mm, the effects of providing the hollow portion such as an increase in the moment of inertia of the golf ball and an improvement in shot feeling cannot be sufficiently achieved.

The outer diameter of the hollow center (2) is 34 to 40 mm, preferably 37 to 39 mm. Outside diameter of hollow center (2) is 34m
If it is smaller than m, the cover becomes thicker and the shot feeling is reduced, and since the specific gravity of the composition used for the cover is usually small, the moment of inertia becomes smaller, and if it is larger than 40 mm, the cover becomes thinner and rebound Decrease.

The thickness of the hollow core including the thickness of the hollow center is at least 4.0 mm, preferably 5.0 to 20 mm. If the thickness of the hollow core is smaller than 4.0 mm, the cover becomes too thick or the diameter of the hollow portion becomes too large.
If the cover is too thick, the shot feeling tends to decrease, and if the diameter of the hollow portion is too large, the resilience decreases as described above.

When the hollow core (5) is composed of the hollow center (2) and the intermediate core layer (3), the thickness of the hollow center is 3 to 15 mm, preferably 5 to 10 mm. When the thickness of the hollow center is smaller than 3 mm, the hollow center is easily deformed in the step of coating the core rubber layer on the hollow center. If the hollow center thickness is greater than 15 mm, two vulcanized bowl-shaped hemispheres are joined with an unvulcanized rubber composition and vulcanized,
In the step of manufacturing the hollow center, the expansion amount due to heating during vulcanization of the bowl-shaped hemisphere becomes large and the hollow center is easily deformed, and the rubber composition for bonding is easily protruded inward, and It is difficult to make the core layer and the cover layer have a desired thickness.

Next, a cover is coated on the hollow core. The cover can be formed of an ionomer resin or balata commonly used as a cover material for a solid golf ball, and a small amount of another resin may be added. As the ionomer resin, a resin obtained by neutralizing a part of carboxylic acid in an ethylene- (meth) acrylic acid copolymer with a metal ion, or a mixture thereof is used. Examples of the neutralizing metal ion include alkali metal ions such as Na ion, K ion, and Li ion; divalent metal ions such as Zn ion, Ca ion, and Mg ion; trivalent metal ions such as Al ion; Nd ions and the like; and mixtures thereof, of which Na ions, Zn ions, and Li ions are often used because of their resilience, durability and the like. Specific examples of the ionomer resin include, but are not limited to, Himilan 1557, 1605, 1652, 1705, 1706, 1707,
1855, 1856 (manufactured by DuPont Mitsui Polychemicals), IOTEC 70
10, 8000 (manufactured by Exxon) and the like.

The cover composition may contain a filler such as barium sulfate, an additive such as titanium dioxide for coloring, and other additives such as an ultraviolet absorber, a light stabilizer and a fluorescent material or a fluorescent material. A whitening agent and the like may be contained in a range that does not impair the desired properties of the golf ball cover, but the amount of the coloring agent is usually preferably 0.1 to 0.5 part by weight.

The cover of the present invention is formed by a generally known method used for forming a cover of a golf ball, for example, injection molding, press molding or the like. When covering a cover, usually, many depressions called dimples are formed on the surface. The golf ball of the present invention is usually coated with paint and put on the market in order to enhance aesthetic appearance and commercial value. The paint is not particularly limited,
Two-part curable urethane paints are preferred because they have good appearance and abrasion. The cover preferably has a thickness of 1 to 4 mm. When the thickness of the cover is less than 1 mm, the strength of the cover is insufficient, and the durability of the obtained golf ball is apt to be reduced. Therefore, the thickness is more preferably 1.5 mm or more. If the thickness of the cover exceeds 4 mm, the shot feeling of the obtained golf ball deteriorates. Therefore, the thickness is more preferably 3 mm or less.
The cover may be composed of two or more cover layers.

According to the method of the present invention, there is provided a hollow golf ball having a true spherical hollow portion, excellent durability, and improved hitting feel without impairing resilience performance.

[0031]

The present invention will be described in more detail with reference to examples.
However, the present invention is not limited to these examples.

(Examples 1 to 7 and Comparative Example 1) Preparation of Hollow Core Rubber compositions having the composition shown in Table 1 below were mixed and kneaded with a roll kneader to obtain hemispherical gold as shown in FIG. Type (11)
Using the core and the hollow core (12), the mixture was heated and pressed at 160 ° C. for 20 minutes to produce a vulcanized bowl-shaped hemisphere (13). The unvulcanized rubber compositions A to F for bonding having the composition shown in Table 2 were arranged and bonded between the two joining surfaces of the obtained bowl-shaped hemispheres, and a mold as shown in FIG. The unvulcanized rubber composition was vulcanized therein to form a hollow center having a diameter of 38.4 mm. The t ₉₀ of the unvulcanized rubber composition for adhesion using the measured temperature of the circular scan meter measures set to 160 ° C., the results shown in Table 5, measuring a hollow portion diameter of the hollow center obtained The results are shown in Table 3. The manufacturing method of each hollow center is shown below. This hollow center was used as a hollow core.

[0033]

[Table 1] (Note 1) High cis-1,4-polybutadiene (contains 96% of cis-1,4 structure) manufactured by JSR Corporation (Note 2) Zinc oxide manufactured by Toho Zinc Co., Ltd.

Method for Preparing Hollow Center (I) An unvulcanized rubber composition for bonding was formed into a sheet having a thickness of 0.5 mm, and was sandwiched between two joining surfaces of two bowl-shaped hemispheres. Using the center hemisphere mold (21), 160
The hollow center was formed by hot pressing at 20 ° C. for 20 minutes. (II) After dissolving the unvulcanized rubber composition for bonding in naphtha, apply it to the joining surfaces of the two bowl-shaped hemispheres and bond them together. Two hemisphere molds for hollow center as shown in FIG. Using (21), a hot center was formed at 160 ° C. for 20 minutes to form a hollow center. (III) An unvulcanized rubber composition for bonding is formed into a sheet having a thickness of 0.5 mm, and is sandwiched between two joining surfaces of two bowl-shaped hemispheres. As shown in FIG. ) Using 130
C. for 5 minutes and then hot pressed at 160.degree. C. for 20 minutes to form a hollow center. (IV) After dissolving the unvulcanized rubber composition for bonding in naphtha, apply it to the joining surfaces of the two bowl-shaped hemispheres and attach them together, and then use the two hemisphere molds for the hollow center as shown in FIG. Using (21), preheating was performed at 130 ° C. for 5 minutes, and then hot pressing was performed at 160 ° C. for 20 minutes to form a hollow center.

[0035]

[Table 2] Type A B C D E F BR-11 (Note 1) 100 100 100 100 100 100 Zinc acrylate 25 25 25 25 25 25 Zinc flower No. 3 (Note 2) 36 36 36 36 36 36 Dicumyl peroxide 2 2 2 2 2 2 Nocrack NS5 (Note 3) -0.5 1 2-0.5 Barnock R (Note 4)----0.5- (Note 1) High cis-1,4-polybutadiene (cis-1,4 structure) manufactured by JSR Corporation (Note 2) Zinc oxide manufactured by Toho Zinc Co., Ltd. (Note 3) Antiaging agent manufactured by Ouchi Shinko Chemical Co., Ltd. (Note 4) Organic sulfur compound manufactured by Ouchi Shinko Chemical Co., Ltd.

Preparation of Cover Composition The cover compounding materials shown in Table 3 below were mixed by a twin-screw kneading extruder to obtain a pellet-shaped cover composition. The extrusion conditions were a screw diameter of 45 mm, a screw rotation speed of 200 rpm, and a screw L / D 35, and the blend was heated to 200 to 260 ° C. at the die position of the extruder.

[0037]

[Table 3] Cover compounding type Parts by weight Himilan # 1605 (Note 5) 50 Himilan # 1706 (Note 6) 50 Titanium dioxide 2 (Note 5) Sodium ion neutralized ethylene-methacrylic acid manufactured by Mitsui Dupont Polychemicals Co., Ltd. Copolymer ionomer resin (Note 6) Zinc ion neutralized ethylene-methacrylic acid copolymer ionomer resin manufactured by Mitsui DuPont Polychemicals, Ltd.

Preparation of Golf Ball On the core obtained as described above, the above-mentioned cover composition was coated by injection molding and painted with a two-part curable urethane paint to form a hollow having a diameter of 42.9 mm and a weight of 45.3 g. I got a golf ball. The shape and durability of the hollow portion of the obtained hollow golf ball were measured, and the results are shown in Table 5. The test method was performed as described below.

(Comparative Example 2) A rubber composition having the composition shown in Table 1 was used at 160 ° C. for 8 hours using a hemispherical mold (11) and a hollow core (12) as shown in FIG. A half-vulcanized bowl-shaped hemisphere (13) is prepared by heating and pressing for half an hour, the core (12) for the hollow part is extracted, and further hot-pressed at the same temperature for 20 minutes to vulcanize the hollow part having a diameter of 15 mm. Center formed. The diameter of the hollow portion of the obtained hollow center was measured, and the results are shown in Table 5. This hollow center was used as a hollow core. Other production methods were the same as in Examples 1 to 7 and Comparative Example 1, on which the cover composition having the composition shown in Table 3 was injection-molded on the obtained hollow core, followed by two-part curable urethane paint. Coating was performed to obtain a hollow golf ball having a diameter of 42.9 mm and a weight of 45.3 g. The shape and durability of the hollow portion of the obtained hollow golf ball were measured, and the results are shown in Table 5. The test method was performed as described below.

Comparative Example 3 A rubber composition having the composition shown in Table 4 below was inserted into two hemispherical molds without using the core mold (32) and vulcanized at 160 ° C. for 20 minutes. With no hollow
An 8.4 mm spherical core was obtained. On the obtained core, the cover composition having the composition shown in Table 3 above was injection-molded, and then covered with a two-component curing type urethane paint to obtain a diameter of 42.9.
mm solid golf ball was obtained. The durability of the obtained solid golf ball was measured, and the results are shown in Table 5. The test method was performed as described below.

[0041]

[Table 4] (Note 1) Hi-cis-1,4-polybutadiene (96% cis-1,4 structure) manufactured by JSR Corporation (Note 2) Zinc oxide manufactured by Toho Zinc Co., Ltd.

[0042] (Test method) using t ₉₀ curastometer (Co. Orientec made of JSR Curastometer type IIID), measured temperature 160 ° C.,
Sample shape, diameter 43mm x thickness 3mm, amplitude angle ± 1 degree, period
Under the condition of 100 cpm (100 reciprocations per minute), the stress in response to the vibration applied to the sample, that is, the change with time of the torque is measured. FIG. 4 is a graph showing the change over time in torque from the unvulcanized state of the measured sample to complete vulcanization,
The higher the torque, the more vulcanization proceeds and the harder the material. Vulcanization torque with the inter gradually increases, the maximum value T _max of the torque at the time t ₁₀₀ to vulcanization completed
Appears. The torque of the sample is 90% of this maximum torque _Tmax
The time required to reach (T _max × 0.9) is defined as t ₉₀ . Hollow Portion Shape For 100 balls obtained as described above, the ball was cut, the major axis and the minor axis of the hollow portion were measured, and the difference between the major axis and the minor axis of the hollow portion was calculated. Evaluate if it is a circle. The evaluation criteria were as follows. Evaluation criteria ○… The average value of the difference between the major axis and the minor axis of the hollow part is within 1 mm △… The average value of the difference between the major axis and the minor axis of the hollow part is less than 3 mm ×… The difference between the major axis and the minor axis of the hollow part The average value of the golf balls was 3 mm or more. Durability A driver was mounted on a swing robot manufactured by True Temper and the number of golf balls that did not crack after being hit 50 times at a head speed of 45 m / sec was expressed as the number of samples (100 samples).
Pieces).

(Test results)

[Table 5] Example 1 2 3 4 5 5 6 7 Unvulcanized rubber blended BCEBFDNt ₉₀ (min) 7 11 10 7 5 17 7 Core molding method II I II II IV hollow diameter (mm) 14.3 14.2 14.4 14.3 14.4 14.3 14.4 〇 85 82 88 81 86 83 82 Hollow shape [pieces] △ 15 18 12 19 14 17 18 × 0 0 0 0 0 0 0 Durability [pieces] 100 100 100 93 100 100 100

[0044]

[Table 6] Comparative Example 1 2 3 unvulcanized rubber A - - t ₉₀ (minute) 2 - - Core molding method III - - hollow diameter (mm) 14.3 12.5 - 〇 85 30 - hollow shape [pieces] △ 15 45 - × 0 25- Durability [pieces] 30 83 100

From the above results, when the hollow golf ball manufacturing method of the present invention is used, a golf ball having a substantially spherical hollow portion and having the same durability as the solid golf ball of Comparative Example 3 can be obtained. You can see that.

The golf ball of Comparative Example 1, the unvulcanized rubber composition for bonding does not use an organic sulfur compound or antioxidant, said before t ₉₀ is small, the hollow center expands sufficiently heat The vulcanization of the unvulcanized rubber composition proceeds, and a sufficient adhesive effect cannot be obtained, resulting in very poor durability. Since the golf ball of Comparative Example 2 was formed by joining two preformed hollow center bowl-shaped hemispheres and performing vulcanization in a mold, the expansion of the rubber compound for the hollow center caused the expansion of the hollow center. Are deformed, the hollow portion is small, and the shape is not spherical.

[0047]

According to the present invention, the hollow portion is a true sphere,
A hollow golf ball having excellent durability and a method for producing the same are provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of the hollow golf ball of the present invention.

FIG. 2 is a schematic cross-sectional view of a mold for forming a bowl-shaped hemisphere used in the method of manufacturing a hollow golf ball of the present invention.

FIG. 3 is a schematic sectional view of a hollow center molding die used in the method of manufacturing a hollow golf ball of the present invention.

FIG. 4 is a graph showing a change over time of a torque of a rubber composition for bonding a bowl-shaped hemisphere of the present invention, measured using a curastometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Hollow part 2 ... Hollow center 3 ... Intermediate core layer 4 ... Cover 5 ... Hollow core 11 ... Hemispheric mold for bowl-shaped hemisphere molding 12 ... Core for hollow part 13 ... Bowl-shaped hemisphere 21 ... Hollow center molding Hemisphere mold

Claims (5)

[Claims] A hollow core (5) comprising a hollow center (2) having a hollow portion (1) and, if necessary, one or more intermediate core layers (3) formed on the hollow center. In the method for producing a hollow golf ball comprising a cover (4) formed on a core, the step of producing the hollow center includes: (a) a step of preparing a rubber composition for the hollow center; Forming a vulcanized bowl-shaped hemisphere by using the rubber composition for use; and (c) disposing an unvulcanized rubber composition for bonding between the joining surfaces of the two bowl-shaped hemispheres. And bonding the unvulcanized rubber composition in a mold to form a hollow center. The unvulcanized rubber composition is formed into a circular sample having a diameter of 43 mm and a thickness of 3 mm. Form and process using a curast meter
The time (t ₉₀ ) until the torque reaches 90% of the maximum torque when measured at the same temperature as the vulcanization temperature in (c) is 5
20 to 20 minutes. 2. The vulcanization in the step (c) is carried out by the t ₉₀
The method for producing a hollow golf ball according to claim 1, wherein the vulcanization is performed for the above vulcanization time. 3. The hollow part (1) has a diameter of 8 to 20 mm,
The hollow center (2) has an outer diameter of 36 to 39 mm.
Or the method of manufacturing a hollow golf ball according to any one of the above items 2. 4. The step (c) comprises the steps of: (i) disposing an unvulcanized rubber composition for bonding between the joining surfaces of the two bowl-shaped hemispheres and bonding them together; ~ 130 ℃
(Ii) expanding the two bowl-shaped hemispheres by heating for at least 2 minutes, and (ii) then vulcanizing the unvulcanized rubber composition at 150 to 180 ° C. to form a hollow center. A method for producing a hollow golf ball according to claim 1. 5. The method according to claim 1, wherein the unvulcanized rubber composition is a sheet or a solution of an organic solvent.